Here’s a quick look at the numbers behind two major statistics you may have heard in the coverage of this important study.

1: Men assigned to active surveillance had twice the risk of cancer progression and spread compared to men who got immediate treatment.

This is why it’s important to know the difference between relative risk and absolute risk. Relative risk is in relation to some other thing (e.g.: “twice as likely”). Absolute risk is what the chances actually are (e.g.: 1 in 6).

So “twice the risk” tells us something important, but not everything important. Absolute risk tells a more complete story.

Among those men who got immediate treatment, three out of 100 saw their cancers progress in ten years.

Among men under active surveillance, the rate was six out of 100.

So immediate treatment (surgery or radiation) did indeed result in half the risk. But the increase in “absolute risk” was 3%, which helps put “twice the risk” into perspective. Also, it’s a reminder that current treatment is not foolproof, and that some cancers progress despite our best efforts.

2: More than half of men undergoing active surveillance ended up receiving treatment anyway.

Based on this stat, it would be easy to say all of the men diagnosed with early-stage prostate cancer using PSA might as well have gotten treatment. But take a closer look at the numbers.

As it turns out, aboutthird of the men assigned to active surveillance decided with their doctors to undergo treatment anyway. And understandably. Imagine the anxiety of knowing there’s a cancer inside you, for years.

Meanwhile, 20% of the men doing active surveillance saw their cancer progress enough to warrant more radical treatment. And just as important: 44% of men made it through the ten years with no progression.

No one’s saying these details change the outcome or conclusion of the study. Seemingly everyone agrees, as my favorite chief medical officer said yesterday, that the study “will help inform [the] discussion for men making what is a highly personal, and often difficult choice.” Let’s be sure, then, that men hear the numbers behind the stats.